Yes, you sholuld definitely start preparing for GATE from now on.

• Starting early will help you focus on the basic concepts. In first two years of engineering, you are new to subjects and you need time to cope up with the concepts. Coming in the third year you will be familiar with the engineering concepts and it will be easy for you to understand new concepts. You will have enough time to work on the basics.
• Most of the high scoring subject in GATE are from 3rd and 4th year of engineering. So if you will start preparing from the 3rd year you with l get double benefit. Before entering the fourth year you will pared well.
• Preparing in advance will help you to cope up easily with the concepts you will be studying in your final year. This advance preparation prevent you from entering a phase of struggle. You will be confident enough to solve problems related to new subjects wherein other students will be struggling to learn those concepts.
• If you start preparing from the 3rd year you will get enough time to gather the best resources to study. You will be able to find the best institute, best books and make proper notes. You would not have to take any decision in hurry.
• Most importantly, starting early will give you enough time for revision. In your final year where you also have other important things on your head, you will not have to spend you entire time on GATE preparation. You can spare out time from your time table for revision. All concepts & tricks will be on your finger tips.